1. Field of the Invention
The present invention relates to an imaging device and a method of driving the imaging device, and more particularly, to an imaging device and a method of driving the imaging device that may obtain a characteristic of high sensitivity both at a low luminance and at a high luminance.
2. Description of the Related Art
An image sensor may operate by receiving incident light using a unit pixel, converting the light to an electrical charge, generating a corresponding voltage signal, and outputting the signal. For example, one parameter indicating a performance of a complementary metal oxide semiconductor (CMOS) image sensor is a dynamic range (DR), which is indicated as a ratio of minimum input signals detectable by the CMOS image sensor to maximum input signals that may not saturate the CMOS image sensor.
However, a conventional color image sensor may have a narrow DR and thus, may not express an original color of an image when at least one of red, green, and blue is in a saturated state. To overcome an issue of the narrow DR, a method of implementing a wide dynamic range (WDR) pixel is proposed.
Conventionally, a method of increasing an electrical charge storing capability, or well capacity, of a photoelectric conversion area included in the CMOS image sensor, or a method of reducing dark current or noise such as fixed pattern noise (FPN) may be used to increase the DR of the CMOS image sensor.
Also, an issue of image distortion may occur when a moving object is captured using a rolling shutter that may sequentially shift, by a row or a line, electrical charges integrated in a photoelectric converter, for example, a photodiode, included in a pixel array. Thus, a global shutter method that may simultaneously shift the charges integrated in the photoelectric converter included in the pixel array may be applied to capture a fast moving object.
However, a pixel used to achieve the WDR may not be suitable for the global shutter method to capture the object. Thus, the conventional image sensor may be used by applying separate methods of using the image sensor suitable for the global shutter method based on an environment in which the image sensor is used or using the image sensor suitable to obtain the WDR.